The invention relates to an electric lamp comprising:
a lamp vessel in which a light source is arranged;
a lamp cap connected to the lamp vessel and provided with electric contacts;
current supply conductors connected to the light source and to respective contacts of the lamp cap;
the lamp cap having a metal shell and a base of insulating material which has an exterior surface which carries a metal disc as an electric contact; and
a current supply conductor issuing through an opening in the base and in the metal disc to the exterior, where it is fixed to the disc with solder.
Such a lamp is generally known and is widely used.
The lamp cap of the lamp may be of the Edison type and may carry a metal disc centrally positioned at the base as an electric contact. Alternatively, the lamp cap may be of the bayonet type. It then has a centrally positioned metal disc or a first and second metal disc as contacts at the base.
A centrally positioned disc, for example in the case of Edison lamp caps, may be as large as 10 or 14 mm in diameter. That is much larger than is required for realising a soldered connection between the relevant current supply conductor and the disc. In the case of bayonet lamp caps having a first and a second disc at the base, the discs may be elliptical with dimensions of, for example, 5.5.times.11 mm. These dimensions are also much larger than is required for rendering a soldered connection possible, but necessary for keeping the contacts touching the contact members of the lampholder when the lamp is inserted in the lampholder, and during relative rotation in the lampholder.
If good soldered joints between a current supply conductor and the relevant metal disc are to be made, it is necessary for a soldering flux to be provided on the heated disc, which flux cleans the disc surface and renders flow and adhesion of the solder possible. The solder flux, for example a solution of ZnCl.sub.2 and NH.sub.4 Cl in glyercol/water, then runs boiling and in an uncontrolled fashion over the entire surface of the disc, and can then run off the disc over the base to the shell of the lamp cap. Soldering flux residues may remain at the base, for example, in hair cracks in the base. They can cause a conductive connection between the metal disc at the base and the shell of the lamp cap, so that the light source of the lamp is short-circuited.
The consumption of soldering flux is high owing to a relatively large surface of a metal disc. In addition, a large cleaned surface entails that the solder can flow over a large surface. This renders the solder consumption high. The random and uncontrolled fashion in which the soldering flux and the solder flow out over the surface of the metal disc, during which it is important whether the disc is flat and whether it is held horizontal, have the result that the shape and the location of the solidified solder can strongly vary in a finished lamp.
It should be noted that GB-1 430 972 discloses a bayonet lamp cap having contacts at its base which are different from conventional contacts as regards shape, dimensions, and position. The contacts each have a first region which is to make contact with contact elements of a lampholder and a second region on which the soldered connection with the relevant current supply conductor is made. These regions are entirely separated from one another by a groove which is to prevent solder flowing out from the second region over the first region.